Cryogenic apparatus



CRYOGENIC APPARATUS Filed Aug. 7, 1961 2 Sheets-Sheet 1 lr wventors:Norman H. Wood, Loyd B. Nesbitt,

- by W 4. 72kg Their- Attorney.

April 28, 1964 N. H. WOOD ETAL CRYOGENIC APPARATUS 2 Sheets-Sheet 2Filed Aug. 7, 1961 Inventors.- Nor'man H. Wood, Loyd B.Nesbit,t,, by WW!9 Their Attorney.

United States Patent 3,136,563 CRYGGENIC APPARATUS Norman H. Wood,Schenectady, and Loyd B. Nesbitt, Alplaus, N.Y., assignors to GeneralElectric Company, a corporation of New York Filed Aug. 7, H61, Ser. No.129,842 7 Claims. (ill. 62-46 The present invention relates to improvedcryogenic apparatus and, more particularly, to improved cryogenicpumping apparatus for use in space simulating chambers.

In the copending application of Donald J. Santeler, entitled, CryogenicPumping Apparatus, filed September 30, 1960, Serial No. 59,642, andassigned to the assignee of the present application, there is discloseda cryogenic pumping apparatus for use in space simulating chambers whichwill substantially permit the duplication of cold black space and thepressure conditions existing in the spatial environment. In the Santelerapplication, it is recognized that molecules being distributed from thesurface of a vehicle in space rarely collide with one another and returnto the vehicle: To duplicate this effect in a confining chamber, such asa space simulator, it is necessary that the walls of the chambersubstantially absorb all the molecules emitted by the space vehicle orthe test member. To simulate spatial conditions, pressures less than 1X10- millimeters of mercury should be maintained and this may be achievedby a three-fold pumping arrangement including mechanical pumping,diffusion pumping, and cryogenic pumping.

Specifically, the Santeler application discloses a cryogenic pumpingconstruction which includes radiant energy absorbing means in the formof a baffle fin which is in heat exchange relation with a refrigerant,such as liquid nitrogen at a temperature of approximately 77 K., tomaintain the temperature of the bafile fin less than approximately 100Kelvin. The baffle fin further shields a condensing fin maintained at alower temperature, for example, K. This low temperature may be achievedby the use of refrigerants such as gaseous helium and liquid hydrogen.The purpose of this shield construction, as noted in the Santelerapplication, is to utilize the baffie fin principally for the absorptionof radiant energy and to use the condensing fin to pump certain gases.If the baflle fin surface is cooled with liquid nitrogen at 77 K., itcryogenically pumps water, carbon dioxide, and hydrocarbons in additionto absorbing radiant energy. Cryoenic pumping as utilized hereingenerally denotes the condensation of a gas or vapor on a lowtemperature surface, the gas substantially remaining on the surface in aliquid or solid state. If liquid hydrogen or gaseous helium is utilizedto cool the condensing fin to approximately 20 K., there iscryogenically pumped nitrogen, oxygen, argon, and carbon monoxide whichleaves only helium, hydrogen, and neon as unpumped gases. In the eventthat liquid helium, at approximately 4 K., it utilized in the condensingfin, then only helium in the chamber will not be pumped.

In our copending application entitled, Improved Cryogenic PumpingApparatus, filed November 2, 1960, Serial No. 66,820, and assigned tothe assignee of the present application, there is disclosed an apparatushaving the previously noted advantages of the Santeler construction butalso having improved means for assuring rapid and effective cryogenicpumping. This improvement is achieved by providing suitable passagesthrough the baffie fin to permit the passage of certain gasestherethrough to the condensing fins. The term condensing as util zedherein with reference to the condensing fin denotes the substantialliquification or solidification of certain gases on the condensing fin,these gases not ordinarily condensing on the radiant energy absorbingmeans, because of their low boiling points.

A study of the previously cited applications discloses a radiant energysource in the chambers for simulating solar radiation. The principalfunction of the bathe fins is to maintain the blackness of the chamber,that is, to make the walls optically black in a manner that radiantenergy when reaching the bafiie fins will be absorbed withoutappreciable reflection. Furthermore, the bafile fins are also black tocertain molecules, that is, in performing tests of the type described,vast quantities of water vapor may be present and these molecules ofwater vapor must be pumped, preferably cryogenically, on the surfaces ofthe baffle fins. After a predetermined time, it is quite possible thatthe gases that are condensed on the bafie fins form a coating of ice onthe surfaces thereof and lose their black quality.

The chief object of the present invention is to provide an improvedspace simulating chamber.

Another object of the invention is to provide improved cryogenic pumpingmeans.

A further object of the present invention is to provide an improvedcryogenic pumping member including a baffle fin which will maintain itsblackness, i.e., high absorptivity, so that it absorbs radiant energyand cryogenically pumps certain gases, such as water vapor, for longperiods of time without substantially reflecting radiant energy andmolecules.

These and other objects of our invention may be more readily perceivedfrom the following description.

One of the features of our invention is a cryogenic pumping constructionfor use in evacuated chambers wherein bailie means utilized mainly toabsorb radiant energy and to cryogenically pump certain gases, such aswater vapor, carbon dioxide, and certain hydrocarbons, includes a memberconstituting a heat-conducting path which maintains the temperature ofextended surfaces associated therewith at desired levels. Theconstruction assures the optical and molecular blackness of the bafflemeans by absorbing radiant energy or molecules on initial contact orupon reflection from an adjacent surface.

The attached drawings illustrate preferred embodiments of the invention,in which:

FIGURE 1 is a view in section of a space simulating chamber employingthe present invention;

FIGURE 2 is a sectional view of a cryogenic member which may be utilizedin the apparatus in FIGURE 1;

FIGURE 3 is a sectional view of another embodiment of the cryogenicmember illustrated in FIGURE 2; and

FIGURE 4 is an enlarged fragmentary plan view of the baffie memberutilized in the cryogenic members illus trated in FIGURES 2 and 3.

In FIGURE 1, a space simulating chamber 2 is illustrated for practicingthe present invention. Space simulating chamber 2 may comprise an outershell including an upper hemispherical shell member 3, a lowerhemispherical shell member 4, and a central cylindrical shell member 5which define the evacuated chamber within which a test member 12 such asa satellite or space vehicle, may be mounted for suitable testing. Inthe upper portion of the chamber so defined, shield 6 may be suitablysuspended for purposes of absorbing radiant energy. Adjacent shield 6may be mounted a radiation source '7 which is intended to duplicate theradiant energy supplied by the sun in outer space. In the lower portionof the chamber, a substantially spherical cryogenic member 8 may bemounted, the spherical member being supported by rods 11 extending fromgusset plates 149. These gusset plates may also support shield 6 withinthe chamber.

A combination of mechanical, diffusion, and cryogenic pumping means maybe utilized to evacuate chamber 2.

The mechanical and difiusion pumping means are located externally ofsimulating chamber 2 and are connected thereto by means of conduitelbows 17 and 18. These elbows may extend through cylindrical portion 5of the housing and one end of each may extend through radiant energyabsorbing shell 6. The opposite ends of elbows 17 and 18 may beconnected to suitable diffusion pumps 20 and 21 which have associatedtherewith mechanical pumping means 22 and 23. The construction andmanner of operation of these difiusion pumps and mechanical pumps are ofa conventional nature and may be of the type described in our previouslyidentified patent application.

In FIGURE 2 there is shown an enlarged sectional view of a portion ofthe cryogenic pumping member 8 illustrated in FIGURE 1. This membercomprises a spherical wall portion 27 which is fabricated of a pluralityof panels 25 having heat exchange coils 26 (also shown in FIGURE 1)connected thereto. Refrigerants, such as liquid nitrogen, may becirculated through coils 26 to cool all the thermally associatedportions of member 8 to maintain them within a given temperature rangeof from 77 to approximately 100 K. These portions may include baffiefins 28, each of which comprises a plate 29 which constitutes a thermalpath from wall member 27 in such a manner that good heat transfer existsthroughout the baffle fin construction. The bafiie fin may furtherinclude honeycomb construction 3i which provides a plurality of surfaceswhich define recesses, the wall surfaces of which are thermallyassociated with the refrigerant passing through coils 26.

Condensing fins 31 may be shielded by the bafile fin constructions whichare angularly mounted on wall portion 27. In order to suitablyrefrigerate the condensing fins 31, a refrigerant may be suppliedthrough coils 32 thermally bonded to the condensing fins.

In the embodiment in FIGURE 3, wall member is substantially planar andhas suitable corrugated portions 34 into which suitable refrigerantcoils 36 may be mounted. These corrugations furthermore may providemounting areas for bathe fins 28' which comprise a plate 29' whichconstitutes a heat-conducting path from coil 36 to honeycombconstruction 3%. As in the embodiment in FIGURE 2, the baffie finsprovide a shielding function for condensing fins 31 which arerefrigerated in this embodiment by refrigerant passing through tubes 32.In this embodiment, the Walls of the honeycomb member are oriented at anacute or oblique angle with respect to the backing plate.

In FIGURE 4 there is shown a plan view of a honeycomb construction Whichmay be utilized with the baffle fin constructions illustrated in FIGURES2 and 3. It can be seen that these baifie fins have honeycomb orientedwalls 41 which define a plurality of hexagonal openings 42.

In the operation of bafile fins and condensing fins as illustratedherein and also in the copending Santeler application and our previouslyidentified copending application, the baffle fins absorb radiant energyand also condense certain gases having boiling points higher than thetemperature of the bafiie fins. The condensing fins condense gaseshaving low boiling points. Preferably liquid nitrogen is utilized torefrigerate the bathe fins and a fiuid such as liquid hydrogen or liquidhelium is utilized to refrigerate the condensing fins. Under suchcircumstances, it is desirable to maintain the bafide fins at atemperature of approximately 100 K. or less and the condensing fins attemperatures in the vicinity or range of approximately 20 K.

Depending upon the test, chamber size, and test member, diiferent sizefins having different characteristics are required. Clearly, a plainbafile fin having a regular, smooth planar surface has limitedcondensing area; however, by making the fin of sufficient thickness, thethermal conductivity through the fin may be very good. In the eventliquid nitrogen is utilized to cool such a bathe fin,

after a predetermined time, if sufiicient water vapor is present withinthe chamber, the surface is coated with a film of ice which may diminishthe blackness or absorptivity of the pumping panels, that is, moleculesand radiant energy may be reflected from the surface toward the testmember.

When utilizing perforated bafile fin constructions as illustrated in ourpreviously identified application, the pumping speed of' theconstruction is extremely good since molecules being pumped by thecondensing fins may pass through the passages provided in each bafiiefin. The thermal conductive path between the end of the fin and theportion adjacent the refrigerant, however, may be insufficient for aparticular application and an excessive temperature difference betweenthe end of the fin and the portion of the fin adjacent the wall and inheat exchange relation with the refrigerant may exist. For example, atemperature difference as great as a few hundred degrees Kelvin may beexperienced. Since the area adjacent the refrigerant may beapproximately K., having a temperature of 306 K. at the end of the finwill make the fin useless for pumping water vapor and similar gaseshaving lower boiling points. A situation arises wherein the moleculesreaching the surface of the baffle fin are reflected and redirectedtoward the test member thereby making the space simulating chamberunsuitable for use.

The present invention provides a novel bafile fin construction,preferably for shielding a condensing fin to permit cryogenic pumping ofcertain gases by the condensing fin while the baffle fin effectivelyabsorbs radiant energy and pumps certain higher boiling point gases thatare present in the space simulating chamber. The present inventionprovides a bafile fin with a thermal conducting path, namely, backingplate 29, which constitutes a portion of the baffie fin and this platehas sufiicient thickness to permit radiant energy to be absorbed at the.

end thereof opposite wall 27 at desirably low temperatures. The bafiiefins, through the thermal characteristics of the backing plate, removethe heat absorbed and maintain the temperature of the adjacent surfacesat levels or; for example, 100 K. i

The honeycomb construction 30 is thermally bonded to the backing plate29. This honeycomb is fabricated of a good thermal conductor treated toobtain a highly absorptive surface. In addition to being opticallyblack, it is also maintained at the temperature close to the refrigeranttemperature in coils 26 by the described action of backing plate 29. Forexample, a temperature -dif-' ferential across the fin may exist in theorder of 35 K. The honeycomb member 30 has a further feature in that thewalls 41 define passages 42 through the honeycomb, these passages whenconnected to the backing plate form with the upper surface 43 of thebacking plate recesses 44. It can be readily seen that the temperatureof these raised portions extending from the backing plate can be main Vtained at desired temperatures, or within the desired temperature range,because of the good conductive thermal path to the refrigerant.Furthermore, walls 41 and surface 43 of the backing plate definerecesses having a plurality of adjacent surfaces whereby molecules andradiant energy particles pass into these recesses and have anopportunity to be reflected to adjacent surfaces in the event thatimmediate absorption does not occur. These particles may bounce from onesurface to another without being reflected to the test member. The finsin FIG- URE 3 function similarly as those described in FIGURE 2,however, under certain circumstances, the angled recesses may be moreoptically opaque.

In the operation of the space simulating chamber, generally a testmember 12 is suspended in the chamber illustrated in FIGURE 1 and issubstantially enveloped by cryogenic pumping member 8. Access openingsprovided in the chamber are sealed and as a result of the action of themechanical and diffusion pumps, a substantially low pressure may beachieved. This pressure may be as low as 1X millimeters of mercury. Arefirigerant, such as liquid nitrogen, may then be circulated throughcoils which are in heat exchange relation with shield 6 therebyabsorbing radiant energy in the upper portion of the chamber andcondensing gas molecules having high boiling points. The random movementof gas molecules continues in the area of the test member accompanied bydegassing of the test member resulting in a distribution of gasmolecules therefrom. Reflected energy also passes toward cryogenicpumping member 8, this energy originating from light source 7. Theradiant energy and also molecules in the area of the cryogenic pumpingmember 8 are absorbed and the cryogenic pumping panels supplement theefforts of the mechanical and diffusion pumping means previouslydescribed. Shield 6 and cryogenic pumping member 8 which are bothcooled, in a preferred example, by liquid nitrogen constitute a heatsink for radiant energy, and for latent heat of condensation of a gascondensing thereon. Those gases which are not condensed on the baffiefins are reflected therefrom and are permitted to pass into the spacesbetween the bafiie fins where they are condensed on condensing fins 31.The effectiveness of the battle fins continues as a result of theextended surface provided by honeycomb portion 30 of each balfie fin.This construction not only provides extended surfaces but as previouslynoted, upper surfaces 43 of plates 29 provide reflective surfaceswhereby in the event that a coating is formed on the surfaces,reflection of molecules or radiant energy culminates in the photon ormolecule being absorbed on a subsequent impingement on a condensingsurface, such impingement being assured by the close proximity of thewalls defining recesses 44 and also by the temperatur at which thesurfaces which define the recesses are maintained.

The maintenance of these low temperature surfaces which define therecesses is assured by the extremely good thermal conducting pathprovided by backing plate 29. The edges of the honeycomb constructionare bonded to this backing plate and as previously noted, each backingplate is connected to wall 27 which is in heat exchange relation withrefrigerant being circulated through coils 26. In the preferredembodiment, liquid nitrogen is supplied through these coils and thetemperature difference between the refrigerant and the tips of thebafile fin may only be in the range of 35-50 K., assuring that thehigher boiling point molecules remaining in the chamber are condensed onthe baflle fin surfaces and also assuring that sufficient surface ispresent so that the coating on the fins does not effectively impede thecontinuing action of the surfaces.

In the preferred embodiment of the present invention, a bafile fin isprovided for shielding a condensing fin utilized for cryogenicallypumping extremely low boiling point gas molecules. The bafile finconstruction not only provides extended heat exchange surfaces but alsoassures optical blackness for absorbing radiant energy and also providesmolecular blackness for assuring that higher boiling point gas moleculespresent in the chamber are condensed with minimum reflection of such gasmolecules. While a honeycomb construction has been illustrated in thepresent application, it will be appreciated that other constructionshaving extended surfaces with closely spaced reflecting surfaces maysupply the desired effect.

While we have described preferred embodiments of our invention, it willbe understood that our invention is not limited thereto since it may beotherwise embodied within the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In a space simulator, means defining a chamber, a pump connected toand adapted to substantially evacuate said chamber, a cryogenic memberbeing located in said chamber and being adapted to substantially envelopa test member in said chamber, said cryogenic member including a wallmember, a plurality of bafile fins extending from said wall member andbeing angularly disposed with respect to said wall member, said wallmember and said bafile fins being thermally connected, a plurality ofcondensing fins being located between said baflie fins and the wallmember whereby the condensing fins are substantially shielded from thetest member, said bafiie fins including a plurality of closely spacedsurfaces defining recesses therein.

2. In a space simulator, means defining a chamber, a pump connected toand adapted to substantially evacuate said chamber, a cryogenic memberbeing located in said chamber and being adapted to substantially envelopa test member in said chamber, said cryogenic member including a wallmember, a plurality of bafile fins extending from said wall member andbeing angularly disposed with respect to said wall member, said wallmember and bafile fins being thermally connected, a plurality ofcondensing fins being located between the baflie fins and the wallmember whereby the condensing fins are substantially shielded from thetest member, said baflle fins comprising a backing plate and aperforated plate thermally connected thereto, said backing plate and thewalls of the perforations in the perforated plate defining a pluralityof recesses.

3. In a space simulator, means defining a chamber, a pump connected toand adapted to substantially evacuate said chamber, a cryogenic memberbeing located in said chamber and being adapted to substantially envelopa test member in said chamber, said cryogenic member including a wallmember, a plurality of baffie fins extending from said wall member andbeing angularly disposed with respect to said wall member, said wallmember and baflle fins being thermally connected, a plurality ofcondensing fins being located between the baffle fins and the wallmember whereby the condensing fins are substantially shielded from thetest member, said baflle fins comprising a backing plate and a honeycombmember thermally connected thereto, said backing plate and honeycombmember defining a plurality of recesses.

4. In a space simulator having means defining a chamber and pump meanslocated externally of said chamber for substantially evacuating saidchamber; the improvements comprising a heat sink located in said chamberand adapted to substantially envelop a test member, the heat sinkincluding wall members, a plurality of baffle fins extending from someof said wall members, each baille fin being obliquely disposed withrespect to the wall member to which it is attached; means for coolingthe heat sink including baffle fins to within a first temperature range,condensing fins mounted between the baffle fins and the wall members,the bafile fins substantially shielding the condensing fins fromradiation originating from a test member located in said chamber, meansfor cooling the condensing fins to a second temperature range lower thansaid first temperature range; a thermal conductor having a honeycombconfiguration thermally connected to portions of the heat sink adaptedto be cooled to within said first temperature range and facing the testmember.

5. In a space simulator having means defining a chamber and pump meansexternal of said chamber for substantially evacuating said chamber, theimprovements comprising a heat sink mounted in said chamber andthermally insulated therefrom, said heat sink adapted to substantiallyenclose a test member, said heat sink including wall members, bafflefins extending from at least one of said wall members, each such bafilefin being mounted in thermal contact with the wall member and at anoblique angle wtih respect to it, heat exchange means connected to theheat sink adapted to maintain the temperature of the heat sink includingwall members and baflie fins substantially within a first temperaturerange, a thermal conductor having a honeycomb configuration thermallyconnected to the heat sink to increase the absorptivity of the heat sinkto radiant energy, a condensing fin mounted between a bafiie fin and thewall member and substantially thermally insulated therefrom, the bafflefinssubstantially. shielding the condensing fins from radiationoriginating from a test member located within the heat sink, and heatexchange means for the condensing fins adapted to main-.

tain the temperature of the condensing fins at a second temperaturerange lower than said first temperature range.

6. A cryogenic member comprising a wall member, a bafile plate havingsides connected at an oblique angle to the wall member, heat exchangemeans connected to the wall member and adapted to maintain the wallmember and baflle plate within a first temperature range, a condensingfin mounted between the bafiie plate and the wall member, heat exchangemeans adapted to maintain the condensing fin within a second temperaturerange substantially lower than first temperature range, and a honeycombmember thermally connected to the bafile plate on the side of the plateopposite that near which the condensing fin is located.

7. A cryogenic member comprising a wall member, a plurality of baffleplates, each baffle plate being connected at an oblique angle to thewall member, heat exchange means connected to the wall member andadapted to maintain the wall member and bafile plates within a firsttemperature range, a plurality of condensing fins with References Citedin the file of this patent UNITED STATES PATENTS 2,831,549 Alpert Apr.22, 1958 2,939,316 Beecher et a1 June 7, 1960 2,947,152 Bloem Aug. 2,1960 2,966,341 Reder Dec. 27, 1960 2,985,356 Beecher May 23, 1961 OTHERREFERENCES Design News, Schrader, May 23, 1960, page 5 relied on,

1958 Vacuum Symposium Transactions, American Vacuum Society,Incorporated, published by Pergamon Press, Incorporated, New York, 1959,pages 140443 of interest.

1. IN A SPACE SIMULATOR, MEANS DEFINING A CHAMBER, A PUMP CONNECTED TO AND ADAPTED TO SUBSTANTIALLY EVACUATE SAID CHAMBER, A CRYOGENIC MEMBER BEING LOCATED IN SAID CHAMBER AND BEING ADAPTED TO SUBSTANTIALLY ENVELOP A TEST MEMBER IN SAID CHAMBER, SAID CRYOGENIC MEMBER INCLUDING A WALL MEMBER, A PLURALITY OF BAFFLE FINS EXTENDING FROM SAID WALL MEMBER AND BEING ANGULARLY DISPOSED WITH RESPECT TO SAID WALL MEMBER, SAID WALL MEMBER AND SAID BAFFLE FINS BEING THERMALLY CONNECTED, A PLURALITY OF CONDENSING FINS BEING LOCATED BETWEEN SAID BAFFLE FINS AND 